1. Field of the Invention
The present invention relates to a push button switch for use in VTRs, audio equipments, wireless equipments, copiers, telephones and the like and particularly suitable as a vehicle-mounted switch such as an automotive power window switch.
2. Description of the Prior Art
In the past, rubber contacts for push button switches have offered the advantages of providing a stabilized switching condition as compared with mechanical type contacts, being excellent in chattering characteristic, and being inexpensive, and thus have been used in various applications including VTRs, audio equipments, wireless equipments, copiers, telephones and the like.
However, a small number of rubber contacts have been used in vehicle-mounted push button switches for the reason that an operating feeling required for the vehicle-mounted push button switches is not provided, that is, the following requirements are not met: (i) a high load and a long stroke for prevention of malfunction; and (ii) a high load, a long stroke, and a clear click feeling enough for an operator to recognize switching.
To attain such an operating feeling, the use of a spring and the like in combination with the rubber contacts has conventionally been considered as shown in FIG. 3.
Referring to FIG. 3, two insulative rubber contacts 2a and 2b are arranged laterally in position on a printed board 1 on which a copper foil pattern is formed and various electronic parts are mounted. A case 3 includes left and right bosses 4a and 4b of tubular configuration in positions corresponding respectively to the rubber contacts 2a and 2b. The case 3 is disposed on the printed board 1 so that the rubber contacts 2a and 2b are positioned within the bosses 4a and 4b, respectively. Columnar pushing plates 5 having an outer diameter substantially equal to or slightly smaller than the inner diameter of the bosses 4a, 4b are disposed on the rubber contacts 2a and 2b, respectively, with their top portions exposed outside the left and right bosses 4a and 4b.
Each of the rubber contacts 2a and 2b includes a disc-shaped contact portion 21 in contact with the corresponding pushing plate 5, a flared portion 22 formed integrally with an upper periphery of the contact portion 21, and a ring-shaped portion 23 formed integrally with a lower end of the flared portion 22, as shown in FIG. 3. Lower ends of the bosses 4a, 4b are pressed against the ring-shaped portions 23 to fix the rubber contacts 2a and 2b in the bosses 4a, 4b without position shift, respectively.
As illustrated in FIG. 3, a tubular boss 7 is integrally formed in an intermediate position between the bosses 4a and 4b on an upper surface of the case 3, and a spring 8 having a length greater than the height of the boss 7 is housed in the boss 7. A sliding element 9 having an outer diameter substantially equal to or slightly smaller than the inner diameter of the boss 7 is fitted in an upper portion of the boss 7, with an upper portion of the spring 8 being housed in a recessed groove 10 formed in a lower surface of the sliding element 9. The sliding element 9 has an upper outer surface processed into a curved configuration, and a key top 11 is placed on the sliding element 9.
The key top 11 includes a generally flat base portion 11a, a slidable-contact portion 11b bulging integrally downwardly from the center of a lower surface of the base portion 11a for slidable contact with an upper end portion of the sliding element 9, a groove 11c formed at the center of the slidable-contact portion 11b and releasably receiving the upper end portion of the sliding element 9, and peripheral side walls 11d formed integrally with front and rear peripheries of the base portion 11a. Although not shown in FIG. 3, the peripheral side walls 11d are supported by an outer surface of the boss 7 for rotation about a support shaft at their lower center, with the entire key top 11 pushed downwardly against the urging force of the spring 8. In operation, for example, when the key top 11 is pressed at its left end, the whole key top 11 rotates about the support shaft. Then the left end of the key top 11 moves downwardly, and the bottom of a left wall of the peripheral side walls 11d presses the corresponding pushing plate 5, which in turn deforms the rubber contact 2a. A disc-shaped conductor 12 applied to a lower surface of the contact portion 21 moves downwardly into contact with a conductive portion of the printed board 1, to close a switch contact. When the key top 11 is pressed at its right end, similar operation is carried out so that the rubber contact 2b is deformed.
This type of push button switch provides a satisfactory switch operating feeling if relation between stroke S and operational load F (F-S diagram) is represented by a curve having a pattern shown in FIG. 4. In the construction of FIG. 3, when the key top 11 is pressed at one end (left end) as shown in broken lines, the sliding element 9 slides in the groove 11c. Resiliency of the spring 8 when the sliding element 9 is removed from the groove 11c generates a peak load F2 shown in the F-S diagram of FIG. 4 to produce the operating feeling.
At this time, the actuating support 2a and 2b act only as contacts.
In the prior art construction shown in FIG. 3, however, the practical operating feeling is determined by composition of the reactive forces of the spring 8 and the rubber contacts 2a, 2b. This results in a plurality of factors determining the feeling, and it is accordingly difficult to provide a satisfactory operating feeling.
Further, the prior art construction comprises a large number of parts such as the spring 8 and the sliding element 9, resulting in increased costs and increased switch size.